Fibrous Packing.—The fibrous packing before referred to is composed of hemp, plaited in a four strand plait and inserted in an open-top trough, along the sides of the saw for a distance about two inches less than the radius of the smallest saw the machine uses.
This packing steadies and stiffens the saw, and also affords a means of adjusting its tension, while the saw is running.
Suppose for example, that the saw is rim bound,[47] and the fibrous packing may be rammed tightly to the saw, as near to the saw rim as possible, and less tight as centre of the saw is approached.
[47] For the principles involved in hammering saws to equalize the tension see [page 69 (Vol. II.)] et seq.
This warms the saw, but makes it warmer at the circumference than at the centre, expanding the circumference, and by equalizing the tension, enables the saw to run straight.
Fig. 3115.
When the packing is to be adjusted, the carriage is run out of the way, and the packing operation is performed by hand, with a caulking tool. The packing and its box, as applied to a rack saw bench is shown in [Fig. 3115], by the dark rectangles. By thus packing the saw to guide it and keep it straight, thinner saws may be used, saws 52 inches in diameter, and having a thickness of but 7 or 8 gauge being commonly employed, and in some cases of 9 gauge.
Saws that are thus packed, produce much smoother work.